Madeleine Tepe Misleh’s last memory with her brother Spencer Tepe, before his shocking killing in December, was on Christmas day, when Tepe beamed at her latest artistic creation: princess dresses for Tepe’s 3-year-old daughter Emilia.

“My brother has always been one of my biggest fans,” recalls Misleh, 35, “[and] one of the biggest fans of my art, so he was always proud.”

Misleh spoke to PEOPLE nearly three weeks after Tepe, 37, alongside his wife Monique Tepe, 39, were found slain in their Columbus, Ohio home. The couple’s 3-year-old and 1-year-old were found in a nearby room, physically unharmed.

The slayings came as a shock to the Tepes’ friends and family, left unable to fathom who would want to harm the “madly in love” couple.

On Jan. 10, police arrested Michael David McKee, 39, who had been briefly married to Monique more than a decade ago. He has been indicted on aggravated murder and burglary charges.

As friends, family and the community reel from the shocking double homicide, Misleh says she is holding on to her memories with her brother — especially their last few days, when they met for Christmas.

“We grew up playing Nintendo 64, and we were playing Mario Kart, and Spencer and Monique got a Nintendo Switch for Christmas,” recalls Misleh. “So the last night I was with them, we were all playing Mario Kart. It was a full circle moment.”

She then shares a funny memory: “We gave them controllers and Spencer and Monique gave us electric toothbrushes,” she laughs.

Ohio Dentist's Sister Speaks Out Weeks After Murders

Misleh, too, was her brother’s cheerleader and supporter. During his time at dental school, she says she let him practice his skills on her.

“I was Spencer’s practice patient for Invisalign, so I was always going up to Columbus while he was in dental school,” she recalls with a laugh.

Spencer, known as the protective brother and son, was also a youth mentor who grew close with his mentee’s family over the decade he worked with them.

His mentee, whom he guided from first grade through high-school, even came to Spencer’s dental school graduation in 2017.

“Spencer was always involved, he was always in a club,” says Misleh. “Always pushing the limits — everywhere.”

Want to keep up with the latest crime coverage? Sign up for PEOPLE’s free True Crime newsletter for breaking crime news, ongoing trial coverage and details of intriguing unsolved cases.

Columbus police have not disclosed a motive behind the killings but say it was a “domestic-violence related” and “targeted” attack.

McKee was arrested near his workplace in Rockford, Ill. and booked into the Winnebago County Sheriff’s Office. He is set to be extradited to Ohio to face the charges.

Prior to his indictment, he told an Illinois judge through a local public defender that he plans to plead not guilty to the murder charges.